1. Technical Field
The present invention relates to an electro-optical device, a driving method thereof, and an electronic apparatus provided with the electro-optical device.
2. Related Art
As an example of an electro-optical device, a liquid crystal display device will be described.
In an active matrix type liquid crystal display device driving a pixel electrode by the use of a thin film transistor (hereinafter, referred to as a TFT), for example, an inversion driving scheme (alternating driving scheme) is generally adopted for inversing a polarity of a driving voltage applied to each pixel electrode in every scanning line or in every data line, or in every frame of an image signal so that the disadvantages of display such as the flicker or the burn-in of the display image are prevented.
It is expected that the disadvantages of display such as the flicker or the burn-in can be removed by employing the inversion driving scheme, because it is believed that application of a direct-current voltage component to the liquid crystal layer and deviation of charges between an element substrate and a counter substrate with the liquid crystal layer therebetween can be suppressed by employing the inversion driving scheme. However, the application of the direct-current voltage component cannot completely be removed by just performing the inversion driving. The disadvantages of display still exist.
That is, even though the inversion driving is performed, the application of the direct-current voltage to the liquid crystal layer or the deviation of charges between the element substrate and the counter substrate occurs. Therefore, countermeasures against these problems are required. In addition, the following two phenomena have been known as sources of those disadvantages of display.
A first phenomenon is a so-called field-through (also referred to as “push down”) phenomenon which causes decrease in voltage of the pixel electrode connected to the drain terminal when the TFT is switched from an ON state to an OFF state. The field-through phenomenon is caused by parasitic capacitance between the gate and drain terminals of the TFT and between the source and drain terminals. Specifically, in this phenomenon, charges stored in a parasitic capacitor and in a storage capacitor are redistributed when the TFT is switched to the OFF state, which causes the pixel electrode to drop in the voltage thereof.
A second phenomenon relates to the direct-current voltage component caused by difference in characteristic between an element substrate and a counter substrate with the liquid crystal layer therebetween. More specifically, the element substrate with the pixel electrode or the TFT thereon and the counter substrate with the counter electrode thereon have electric characteristics in an asymmetric manner, so the deviation of charges between the element substrate and the counter substrate occurs.
In JP-A-2002-189460, a method of driving the liquid crystal display device paying attention to two phenomena described above is proposed.
In the driving method described in JP-A-2002-189460, a counter electrode potential serving as the basis for inversing the polarity in the inversion driving is shifted in advance in order to reduce the influence caused by the first phenomenon (field-through) and the second phenomenon (the electrical characteristic difference between the element substrate and the counter substrate).
Specifically, in an early stage, an amount of change in voltage caused by the first phenomenon and an amount of change in voltage caused by the second phenomenon are measured under predetermined measurement conditions, and a value obtained by adding these amounts is added to a set potential of the counter electrode as a correction voltage. The correction voltage is not variable, but fixed.
FIG. 27 is a plot illustrating a relation between a correction voltage and a driving voltage for a second phenomenon. According to experimental data obtained by inventors, since the correction voltage for the second phenomenon and the driving voltage has a correlative relationship to each other, the disadvantages of display, such as the flicker and the burn-in of the display image, occur in the known driving method disclosed in JP-A-2002-189460.
FIG. 27 is a plot illustrating an example of an experimental result obtained by the inventors, and shows the correlative relationship between the driving voltage (horizontal axis) and the correction voltage (vertical axis).
Here, the correction voltage at 10V of the driving voltage is −0.1V, the correction voltage at 5V becomes −0.05V, and the correction voltage at 0V becomes 0V.
That is, in the second phenomenon, the correction voltage depends on the driving voltage. Further, since the driving voltage is changed according to a gray scale to be displayed, the correction voltage which might depend on display contents may be changed between about −0.07V to 0V during performing display in a case where the peak voltage of the driving voltage is 7V.
In addition, a slope of the graph shown in FIG. 27 is applicable to another driving voltage. For example, when the peak voltage of the driving voltage is 15V, the correction voltage at 15V of the peak voltage becomes −0.15V (=−0.1×1.5).
Here, suppose that in the conventional technology the counter electrode potential is determined taking −0.04V as a constant correction voltage by summing up −0.01V of a correction voltage for the first phenomenon and −0.03V of a correction voltage for the second phenomenon.
First, when the driving voltage is 0V, the correction voltage for the second phenomenon should be 0V, but the correction voltage is set to be −0.04V. That means −0.03V of the excess correction voltage is applied as the direct-current voltage component.
In addition, when the driving voltage is 7V, the correction voltage for the second phenomenon should be −0.07V, but the correction voltage for the second phenomenon is set to be −0.03V. That means the differential voltage of −0.04V is applied as the direct-current voltage component. Here, the first phenomenon is considered to be canceled.
As such, in the known driving method in which the constant correction voltage is used to compensate the direct-current voltage components caused by the first phenomenon and the second phenomenon, application of the direct-current voltage to the liquid crystal layer is not fully suppressed, and the disadvantages of display such as the flicker still occur.
In the known driving method, the correction voltage obtained by adding the voltage change amounts of the first phenomenon and the second phenomenon is added to the counter electrode potential. However, when the correction voltage for the second phenomenon is larger than the correction voltage for the first phenomenon to some extent, the counter electrode potential is largely shifted to the positive or negative potential, which is acting as a cause for occurrence of the disadvantages of display.
Specifically, when the correction voltage for the second phenomenon is large, the amplitude difference between the positive and negative driving voltages increases. For this reason, the disadvantages of display such as the flicker occur.